This invention relates to a planetary drive system for a vehicle. Specifically, this invention relates to a transmission used to power vehicles that steer by changing the speed of the wheels on one side of the vehicle relative to the wheels on the other side of the vehicle.
Typically, in lawnmowers, skid loaders and the like have vehicle steering that allows the changing of wheel speed on one side of the vehicle relative to the other and in some instances one side can actually be reversed while the other side travels forward such that the vehicle can execute a zero turn. This is commonly accomplished by using three different differentials. They are often times powered by hydraulic motors or pumps. Specifically, lawnmowers use a pair of hydraulic motors wherein one motor is attached to one side wheel and the other is attached to another side wheel. The motors can be reversed and speed adjusted to control the vehicle.
These systems are complicated and expensive. The most cost effective method of powering a lawnmower is by use of a transaxle. A transaxle is a box containing the gears to drive the machine at the required speed. The transaxle has a single input that is usually a pulley driven by the engine and a pair of axles that attach directly to the wheels of the machine. Thus, no chains or external gear boxes are required.
A disadvantage of using hydraulic drives and other methods is the attempt to synchronize the two drives when it required that the vehicle travel in a straight line. Lack of mechanical connection causes drift and constant adjustment to the travel direction is required by the operator. Other disadvantages of the hydraulic drives are the waste of power due to losses required to circulate the oil. In addition, internal leakage leads to loss of efficiency. Further, the hydraulic drives have a tendency to sustain damage when started in very cold temperatures and additionally the motor can sustain damage when the vehicle is moved with the engine turned off.
Additional disadvantages of current systems include that the available torque from the motors is too low to directly drive the transaxle to the wheel and a secondary speed reduction system must be used between the hydraulic motor and the axle. If this is not done, a large motor must be used. Unfortunately, the savings offered by the small motor is often offset by the requirement of employing a gear reduction to increase the torque. Thus, a need in the art exists for alternative methods to using such hydraulic motors that are presently within the art.
Thus, a principle object of the present invention is to provide a gear drive system for providing a zero turn transmission.
Yet another object of the present invention is to provide an inexpensive method of manufacturing the gear drive system.
Another object of the present invention is to provide a gear drive system that is both inexpensive and easy to manufacture.